“Enemies: The President, Justice & the F.B.I.” goes beyond ripped-from-the-headlines. It’s waiting for the headlines. With the Sword of Donald possibly hanging over the head of the special counsel, Robert S. Mueller III, Showtime attached a disclaimer to screeners of the fourth and final episode, saying it “will be updated to reflect current events in D.C.”

Television documentaries these days are often about President Trump even when they aren’t. It’s unlikely that multiple shows would signal the 20th anniversary of Bill Clinton’s impeachment if the current office holder were less controversial. Charles Ferguson’s Watergate documentary series for the History Channel never mentioned Trump, but he was always there, just outside the frame.

“Enemies,” arriving Sunday and directed by Jed Rothstein and the prolific Alex Gibney, doesn’t hesitate to talk about Trump — the in-progress fourth episode is entirely about his relationship with James Comey, the F.B.I. director he fired shortly after his inauguration.

And he pops up in the earlier episodes, hourlong case studies of Watergate, Iran-contra and the scandals of the Clinton years: Cut from Trump complaining about a witch hunt to Clinton’s being questioned about Monica Lewinsky. Cut from Ronald Reagan denying knowledge of arms-for-hostages to Trump denying collusion with Russia.

Based on the book “Enemies: A History of the F.B.I.” by Tim Weiner, a former investigative reporter for The New York Times, the series is more a survey course than a graduate seminar. Dramatic anecdotes and striking juxtapositions are more plentiful than deep analysis or striking insights.

That’s not to say it isn’t serious — and more than a little alarmist — but it doesn’t take itself too seriously. It’s punchy and to the point. In the historical episodes, it has some of the style and entertainment value of a breezier series on basic cable. A section on J. Edgar Hoover and the rise of the F.B.I. includes a priceless image of shirtless agents on the firing range, taking target practice while doing headstands and back bends.

The interview subjects include Weiner and a number of retired F.B.I. agents, and each chapter is recounted through the prism of the bureau’s involvement. This can be disconcerting — it’s a new and not entirely convincing experience to see Watergate recounted with little or no reference to The Washington Post, the federal judge John Sirica or the Senate Watergate Committee. The F.B.I. played an important role in each of the series’s stories, but it wasn’t always central to an overall understanding of them.

The larger story Gibney and his colleagues are telling is about the misuse of presidential power and the lies that are characteristically told to cover it up. Initially it’s the story of how those lies are uncovered, with the bureau’s help. In the present, the issue becomes whether anyone has the willpower and a sufficient sense of honor to fight against lies that are already out in the open.

The supersized final episode (the preview cut is 97 minutes) looks back to the days after the 9/11 attacks, when a separation between the White House and the Justice Department that had existed since Watergate began to break down. Comey, then the deputy attorney general, and Mueller, then the director of the F.B.I., pushed back against the Bush administration’s domestic surveillance program.

The series’s most engrossing sequence recounts the infamous 2004 encounter in the hospital room of the attorney general John Ashcroft, when administration members tried unsuccessfully to get Ashcroft to renew the surveillance program. Ashcroft, the Bush chief of staff Andrew Card and the Justice Department lawyer Jack Goldsmith, who were all in the room, give their accounts, alongside extracts from Comey’s memoir. (Comey declined to be interviewed for the series.) Emotions are still raw, and memories are conflicting. The one thing that seems clear is that the real hero, if there was one, was Ashcroft’s wife, Janet.

The series is firmly on the side of limiting presidential power and holding presidents accountable when they break the law, though it gives screen time to figures whose views on the subject are ambiguous or openly contrarian, like the Reagan-era attorney general Edwin Meese and the Nixon and Trump ally Roger Stone.

In the course of the final episode, while Comey’s motives and missteps are being dissected, the gloves fully come off with regard to Trump. As it stands, Weiner closes the series declaring that political institutions and the rule of law “are under attack by the president of the United States.” You’ll have to check back in four weeks to see if that’s still the last word.

Correction:

An earlier version of this article misstated the given name of an ally of President Trump’s. He is Roger Stone, not Robert.

“Enemies: The President, Justice & the F.B.I.”Sunday on Showtime

A version of this article appears in print on , on Page C5 of the New York edition with the headline: The Names Change, but the Story Hasn’t. Order Reprints | Today’s Paper | Subscribe